opening.owin {spatstat} | R Documentation |
Perform morphological opening of a window
opening.owin(w, r, ..., polygonal=TRUE)
w |
A window (object of class "owin" . |
r |
positive number: the radius of the opening. |
... |
extra arguments passed to as.mask
controlling the pixel resolution, if a pixel approximation is used |
polygonal |
Logical flag indicating whether to compute a polygonal
approximation to the erosion (polygonal=TRUE ) or
a pixel grid approximation (polygonal=FALSE ).
|
The morphological opening (Serra, 1982)
of a set W by a distance r > 0
is the subset of points in W that can be
separated from the boundary of W by a circle of radius r.
That is, a point x belongs to the opening
if it is possible to draw a circle of radius r (not necessarily
centred on x) that has x on the inside
and the boundary of W on the outside.
The opened set is a subset of W
.
For a small radius r, the opening operation has the effect of smoothing out irregularities in the boundary of W. For larger radii, the opening operation removes promontories in the boundary. For very large radii, the opened set is empty.
This function computes the opening of the window w
as a binary pixel mask. If w
is not already a mask, it is first
converted to a mask by as.mask
. The arguments
"..."
determine the pixel resolution. There is a sensible
default.
The algorithm simply applies erode.owin
followed by
dilate.owin
.
Another object of class "owin"
representing the
opened window.
Adrian Baddeley adrian@maths.uwa.edu.au http://www.maths.uwa.edu.au/~adrian/ and Rolf Turner r.turner@auckland.ac.nz
Serra, J. (1982) Image analysis and mathematical morphology. Academic Press.
closing.owin
for the opposite operation.
dilate.owin
, erode.owin
for the basic
operations.
owin
,
as.owin
for information about windows.
data(letterR) v <- opening.owin(letterR, 0.3, dimyx=256) plot(v, main="opening.owin") plot(letterR, add=TRUE)